Wire coated with boron nitride and boron



June 24, 1969 R. L. HouGH I WIRE COATED WITH BORON NITRIDE AND BRON Filed Oct. 6, 1965 United States Patent O U.S. Cl. 117-69 5 Claims ABSTRACT F THE DISCLOSURE A filament comprising a tungsten wire successively coated with layers of boron nitride and boron. Such filaments are useful wherever high strength-to-weight components are needed.

The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to filaments, yarns of filaments, and the like, and more particularly to a flexible metal filament and yarn coated with boron with a diffusion barrier boron nitride bonded between the substrate and its Iboron coat and to a method of manufacture.

The problems that this invention solves concerns the production and the use of amorphous boron filaments. The filaments have been produced heretofore by chemically vapor plating elemental boron on a flexible wire core substrate of tungsten or the like, heated to from 1700 F. to 2100 F. One very serious limitation of the filaments so 2l00 F. One very serious limitation of the filaments so produced is that during the process the boron diffuses down into the metal causing the tungsten wire to expand and to press outwardly against the growing boron surface deposit causing ever increasing mechanical stresses to build up and to remain in the coated filament. The resulting boron coated filament is highly stressed near the expanded tungsten wire substrate and the core is extremely brittle. The resultant boron filaments are characterized by inherent and deleterious built-in stresses and resultant mechanical weaknesses.

The process that is here described is sponsored by the knowledge that boron nitride is extremely inert toward both tungsten and boron, within the temperature range of this process. Horn has zone melted boron in boron nitride boats, as reported in the Journal of Applied Physics, vol. 30, page 1612, published in 1959. Seybolt has prepared boron and boron-rich alloys in boron nitride, as reported in Transactions of the American Society of Metals, vol. 52, Reprint No. 135, published in 1959.

It has been found experimentally that the synthesized filament core of tungsten, when protected by the thin boron nitride diffusion barrier that is described herein, may be bent easily without breaking. The fracture pattern of the amorphous boron coating applied to the tungsten core with a thin layer of boron nitride positioned therebetween displayed no evidence of internal stresses near the coating substrate interface.

The present invention teaches that a thin boron nitride layer, when deposited upon a fine metal wire, acts as a diffusion barrier for a subsequently deposited layer of amorphous boron to produce an amorphous, unstressed boron filament. When the amorphous boron coating on the substrate wire is relatively thick the absence of internal stresses is of increased importance to the dependable performance of the filament. The resultant boron filament, containing a flexible metal wire core rather than an expanded and embrittled core, can easily be spliced in operations such as filament Winding and the like, Whereas boron filaments without the diffusion barrier protected core are easily fractured.

The presence of the flexible core prevents complete disintegration of the filament at any point of boron fracture.

Thus in a multple columned strand, such as those used in filament Winding, a fractured filament is retained in the strand with additional support from surrounding filaments, all to the advantage of the process and the product that are herein disclosed.

The flexible cored boron fibers, filaments or yarn that embody this invention find extensive use in atomic reaction materials, in filament wound structures such as rocket motors, pressure vessels and the like, and wherever high strength-to-weight components are of importance. Boron fibers are a high priority item for the United States Air Force. Filaments with unstressed flexible cores increase the dependability of hand built elements and components wherever they are used.

This invention has as an object the provision of new and improved amorphous boron filaments that are characterized by highly desirable structural and mechanical properties that have not been available previously in this type of product.

Another object of this invention is the provision of an advantageously continuous process for the manufacture of structurally improved amorphous boron filaments.

A further object of this invention is to provide a dependable product of undeviating uniformity of characteristics in large scale production.

An illustrative embodiment of the present invention is shown in the accompanying drawing, wherein:

FIG. l is a diagrammatic presentation of the apparatus used in the continuous manufacture of the present filament; and

FIG. 2 is a fragmentary, enlarged, partially sectioned filament that embodies the present invention as a. product made with the apparatus shown in FIG. 1.

In the accompanying drawing a fine metal wire filament 10 of tungsten or the like, is passed from a supply spool or the like, not shown, from the left into the interior of a first chamber or furnace 11 that is maintained at a temperature about within the range of from 1500 F. to 2800 F. A desired plurality of gas supplies are fed into the furnace 11, such as from tanks of beta-trichloroborazine 12, a carrier gas 1-3, and a reactive reducing gas 15 such as hydrogen, or the like. The delta symbol 14 indicates the application of heat to the beta-trichloroborazine in the container or tank 12 for its vaporization.

Illustratively, lthe filament 10 has a diameter in the order of about 0.0005 inch. The metal wire 10y is drawn into the furnace 11 containing the vapor of beta-trichloroborazine or beta-TCB for brevity, at a vapor pressure about within the range of from 0.01 mm. to 1001 mm. Hg and with or without the addition of one or more inert carrier gases, of which argon is illustrative and with or without the addition from the reducing gas tank 15, of hydrogen or the like.

Within the furnace 11 the metal wire filament 10 acquires a coating of BN14 according to the reaction:

The metal wire filament 10 also may have a coating of BN applied thereto, if preferred, by the use of the teachings of my application Ser. No. 454,225, filed May 7, 1969, now U.S. Patent '3,401,423 or by techniques known to the art, such as that described in the Patent No. 3,152,006, issued to M. Basche on Oct. 6, 1964, and the like.

The fine metal wire filament 10 with its coating 16 of boron nitride illustratively of a thickness of from 0.1 to 10 microns passes out of the furnace 1.1 and into the furnace 17. The interior of the second chamber or furnace 17 is maintained at a temperature about within the range of 1700 F. to 2100 F., a pressure about atmospheric and an atmosphere of a boron halide and hydrogen that are passed into the furnace 17 from the supply tanks 18 and 19, or the like.

Within the furnace 17, a layer 20 of amorphous metallic boron is deposited as the surface coating on top of the boron nitride 16 covering the wire 10 on its entrance into 4the furnace 17. The equation of the boron deposition within the furnace 17 is In a specied embodiment of the present invention, a ne tungsten metal wire of `0.0005 inch diameter was heated at 220 F. in the furnace 11 for four minutes in the vapors of beta-trichloroborazine from the tank 12. The vapors of the beta-trichloroborazine were obtained by the heating of solid beta-trichloroborazine to 150 F. in a stream of hydrogen flowing at the rate of 125 milliliters per minute. The temperature of the wire 10 was maintained at 2200o F. during the deposition in the furnace 11 of the barrier layer 16 of BN on the line metal filament wire 10.

The wire 10 bearing its boron nitride barrier layer 16 was passed from the furnace 11 into the furnace 17. The boron nitride coated tungsten wire from the furnace 11 was passed into the furnace 17 maintained at 1900 F., at a ow rate that permitted a dwell time of 10 minutes within the furnace 17.

Within the furnace 17 the boron nitride coated tungsten wire 10 was exposed to a stream of hydrogen gas liowing at the rate of 250 milliliters per minute and containing 8 volume percent of boron tribromide. The product drawn from the furnace 17 was coated with a surface layer 20 of boron, such that its diameter was `0.0015 inch. Boron coats of greater thickness were accomplished by miX- tures of boron trichloride and hydrogen in the ratio of two to three parts by weight boron trichloride to hydrogen. Where preferred, higher gas flow rates and slightly higher temperatures, not to exceed 2l00 F., may be used.

The product withdrawn from the furnace 17 is an amorphous boron iilament containing a flexible tungsten wire core 10, the diffusion barrier boron nitride bonding layer 16 and the boron outer coat 20, as illustrated in FIG. 2 of the drawing.

Fracture patterns of the amorphous boron filament product of the furnace 17 indicate no evidence of stress throughout its internal structure.

I claim:

1. A line wire yarn of filaments coated with boron nitride surfaced with boron.

2. The iine wire filament bearing a boron coat with a barrier layer of boron nitride between the filament and the boron coat.

3. The ilament comprising a filament tungsten core, a boron nitride barrier layer overlying the surface of the tungsten core as a protective coating for maintaining the exible characteristic of the tungsten core, and a boron surface coat protectively overlying the boron nitride barrier layer.

4. The method of applying successive coats of boron nitride and metallic boron on a tungsten filament comprising the steps of (a) passing the tungsten filament through a beta-trichloroborazine vapor at a temperature about within the range of from 1500o F. to 21800 F. to deposit boron nitride on said iilament and thereafter (b) passing the resulting boron nitride coated filament into boron halide and hydrogen vapors maintained at a temperature of between 1700 F. and 2100 F. to deposit a surface coat of metallic boron.

5. The method of claim 4 in which the boron nitride is deposited over a period of about 4 minutes and the boron is deposited over a period of about 10 minutes.

References Cited UNITED STATES PATENTS 2,952,599 9/1960 Suchet. 3,131,089 4/1964 Grulke et al 117-106 X 3,152,006 10/1964 Basche 117--106 3,321,337 5/1967 Patterson 117-69 X 3,351,484 11/1967 GutZeit i 117-106 3,359,468 12/1967 Patterson et al. 117-217 X OTHER REFERENCES Powell et al., Vapor Plating 1955, pp. to 97, 101 and 1038 to 109 relied upon.

ALFRED L. LEAVITT, Primary Examiner.

A. GOLLIAN, Assistant Examiner.

UJS. C1. X.R. 117-106, 128 

